Re: making a qdev bus available from a (non-qtree?) device

[Stefan Hajnoczi]

On Wed, May 12, 2021 at 02:02:50PM +0200, Markus Armbruster wrote:
> Klaus Jensen <its@irrelevant.dk> writes:
> > I can then call `qdev_set_parent_bus()` and set the parent bus to the
> > bus creates in the nvme-subsys device. This solves the problem since
> > the namespaces are not "garbage collected" when the nvme device is
> > removed, but it just feels wrong you know? Also, if possible, I'd of
> > course really like to retain the nice entries in `info qtree`.
> 
> I'm afraid I'm too ignorant on NVME to give useful advice.
> 
> Can you give us a brief primer on the aspects of physical NVME devices
> you'd like to model in QEMU?  What are "controllers", "namespaces", and
> "subsystems", and how do they work together?
> 
> Once we understand the relevant aspects of physical devices, we can
> discuss how to best model them in QEMU.

One specific question about the nature of devices vs subsystems vs
namespaces:

Does the device expose all the namespaces from one subsystem, or does it
need to be able to filter them (e.g. hide certain namespaces or present
a mix of namespaces from multiple subsystems)?

The status of the namespace as a DeviceState is a bit questionable since
the only possible parent it could have is a device, but multiple devices
want to use it. I understand why you're considering whether it should be
an --object...

Stefan

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